Question

The crystalline salt, $N{a}_{2}S{O}_{4}x{H}_{2}O$ on heating losses $55.9\%$ of its weight. The formula of the crystalline salt is :

• A. $N{a}_{2}S{O}_4.5H_{2}O$
• B. $N{a}_{2}S{O}_4.7H_{2}O$
• C. $N{a}_{2}S{O}_4.10H_{2}O$
• D. $N{a}_{2}S{O}_4.2H_{2}O$

Answer 1

Answer: (C)

$N{a}_{2}S{O}_4.10H_{2}O$

$N{a}_{2}S{O}_4.x{H}_{2}O$

Mass of hydrate $=23\times 2+32+64+18x$

$=46+96+18x$

$=142+18x$

Mass of water of hydration=$18x$

% of water in hydrate=$55.9$%

$\frac{18x}{142+18x}\times 100=55.9$

$1800x=7937.8+1006.2x$

$793.8x=7937.8$

$x=9.99\sim 10$

Answer= $N{a}_{2}S{O}_4.10H_{2}O$